Translation:Hoşça kalın baykuşlar!
It's an imperative sentence which literally means stay nicely!. So when you are in a formal/polite situation or when you address more than one person you have to use the 2nd person plural ending for imperative which is -In.
Hello deorme90. I stumbled across italics which is *. How did you write in bold?
My version is slightly different. 'ın' here is required because there is more than 1 baykuş.
Looks like Turkish doesn't have a particle used for addressing somebody else in speech like "O" in English or "ya" in Arabic. (eg, "ya akhi" = "O my brother!") Is that right?